The present invention relates to the field of slurries for use in chemical mechanical polishing (planarization) CMP of metal films of semiconductor wafers and, more specifically to a polishing slurry for copper films.
The use of chemical mechanical planarization (CMP) in semiconductor manufacturing is well known to those of skill in the art. For example, CMP processing can be used to remove excess metal, such as copper, used to form interconnects, vias and lines. In one embodiment, the copper layer is formed over a dielectric layer such as a silicon dioxide layer. In another embodiment a barrier layer is formed between the silicon dioxide layer and the copper layer.
In a typical CMP process, a substrate (wafer) having, for example, a copper layer formed over a dielectric layer, is placed in contact with a rotating polishing pad attached to a platen. A CMP slurry, comprising an abrasive and chemically reactive mixture, is supplied to the pad during the CMP process. During the CMP process, the pad and substrate are rotated while downward pressure is applied by the pad against the wafer. The CMP slurry assists in the planarization of the wafer by chemically and mechanically interacting with films on the wafer as the pad moves relative to the wafer.
When the pad is not moving over the wafer, the chemical components of the CMP slurry can continue to remove films on the substrate. For example, copper can be dissolved by the chemical components of the CMP slurry absent any mechanical action by the polishing pad or slurry's abrasive. The removal rate of copper in the absence of any mechanical action is known as the static etch rate of copper. A large static etch rate can lead to problems such as the uneven removal of copper formed on the wafer such as copper trenches and copper vias. This uneven removal is known as dishing. A related problem is erosion, where excess material of the dielectric layer and the copper layer are removed.
Various slurries for the CMP of copper have been disclosed. For example, U.S. Pat. No. 6,396,543, entitled “CMP Method Utilizing Amphiphilic Nonionic Surfactants”, which issued on Aug. 30, 2005 to Schroeder et al., discloses a slurry that includes an amphiphilic nonionic surfactant which is said to reduce dishing. The slurry of this patent is said to decrease dishing to around 1500 Å) for a 100 μm region. While this represents an improvement in dishing, it is still unacceptably high.
Accordingly, it is desired to provide a CMP slurry that has a low static etch rate to help minimize dishing and erosion. Furthermore, the desirable features and characteristics of the present invention will be apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.